The present invention is directed, in general, to an optical device and, more specifically, to an optoelectronic device having a direct patch mask formed thereon, and a method of manufacture therefor.
As optical communications advance, more and more passive optical components are needed, e.g., broadband multiplexors are needed for delivering voice and video to the home, for combining pump and signals in an optical amplifier and for adding a monitoring signal to the traffic on optical fibers. Dense wavelength division multiplexing (WDM) systems need multiplexers to combine and separate channels of different wavelengths and also need add-drop filters to partially alter the traffic. Splitters and star couplers are used in broadcast applications. Low speed optical switches are needed for sparing applications and network reconfiguration.
Currently, silica-based integrated optical waveguide technology is well known and used in the industry for the above mentioned devices. A typical silica-based integrated optical waveguide may comprise a silicon substrate having an undoped silica base layer located thereon. Also, a phosphorous doped and/or germanium core layer is typically located over the base layer. The core layer is patterned and etched to form individual cores. A boron/phosphorous doped silica glass cladding layer may also be blanket deposited over the individual cores.
One problem associated with current optical waveguide technology is birefringence. Since core layers and cladding layers are typically made of different materials, they often have different refractive indices. For example, the core material may comprise a phosphorous doped silica layer and the cladding may comprise a borosilicate glass. The two layers have different thermal expansion coefficients, such that when the molten fiber solidifies after deposition and. annealing, stresses are introduced and frozen into the materials. These stresses tend to cause birefringence of the transverse electric mode (TE) and the transverse magnetic mode (TM). Birefringence often results in polarization dependent wavelength (PDW). PDW is a shift in the center wavelength between the TE and TM modes. For most applications, and especially system applications, this polarization. is undesirable because it generally requires that the two modes be matched.
Currently, one technique used by optoelectronics suppliers uses ultraviolet light and an independent patch mask to correct birefringence. The patch mask commonly comprises a glass substrate having a patterned metal layer formed thereon. The pattern in the metal layer typically mirrors the location of the previously discussed cores, i.e., the metal layer has been patterned and etched to leave unprotected areas over where the cores are located. After the patch mask has been manufactured, the patch mask is visually placed over the device. Ultra violet (UV) light is then projected through the mask, which alters the properties of the film.
Using the patch mask to correct birefringence, as previously described, currently encounters certain problems. One problem results from manual placement of the patch mask over the device. Currently, a window in the patch mask is used to manually align a cross hair in the window with an alignment mark previously manufactured in the device. This manual aspect tends to cause distortion, and furthermore, requires additional unwanted wafer real estate to form such alignment marks.
Another problem is UV intensity variations across the waveguide. This is assumed to be a result of inconsistencies in the glass substrate as the UV light passes through the glass. Another problem is dispersion of the UV light. As with any process requiring passing particles through a pattern to affect a separate surface, the further the pattern is away from the separate surface, the more the dispersion of the particles that results. Inherent in the conventional patch mask process is the glass substrate, on which the patterned metal layer is formed. The glass substrate, located between the patterned metal layer and the separate surface, typically causes such dispersion.
Accordingly, what is needed in the art is a passive optical component that does not experience the prior art""s problems associated with correcting birefringence, and a method of manufacture thereof.
To address the above-discussed deficiencies of the prior art, the present invention provides an optoelectronic device with superior qualities. The optoelectronic device includes an optical core feature located over a substrate, an outer cladding layer located over the optical core feature and a direct patch mask located and formed on an outer cladding layer. In an exemplary embodiment of the invention, the direct patch mask has a light source passed therethrough that corrects birefringence in the optical core feature and the outer cladding layer.